: This study attempts to improve the aerodynamic performance of a delta wing. Delta wings have a different function compared to the other wings due to having a vortex pair that forms along the leading edge of the wing. This vortex pair has a great effect on the aerodynamic performance and flow over the wing surface. Among the factors affecting the flow and vortices formed on the wing, the shape of the wing leading edge can be mentioned. In this study, the effect of needle vortex generators on the flow of a delta wing with a sweep angle of 65° was studied. The experiments were performed at three angles of attack of 10, 15 and 20 degrees at a speed of 20 m/s on two delta wings with and without equipped needle vortex generators at the leading edge. In the first part of the experiments, a five-hole probe was used to investigate the flow and changes of the vortices on the wing surface, at six sections perpendicular to the wing surface and three different attack angles. In order to use the five-hole probe, a calibrator system was designed and built, by which the five-hole probe was calibrated in the wind tunnel test section. To study the effect of air velocity on the vortices formed on the wing, the experiments were performed in a fixed section at two different speedsof 13.5 and 20 m / s. The results of this section were displayed in the form of total pressure contours, velocity vectors and flow lines. Using the results of the five-hole probe, the position of the vortex core was extracted and the velocity fluctuations, spectral power density of the core and axial velocity changes at the six sections of the main vortex were investigated by a hot wire flowmeter. Smoke and laser flow visualization were used to better understand the effect of the vortex generator on the flow over the delta wing. For smoke flow visualization, a smoke tunnel was designed and constructed and the flow visualization tests were performed at six longitudinal sections, six transverse sections and one wing surface section in three different attack angles. Vortex breakdown location changes with time and sequence area were also examined and compared by flow visualization results. The results showed that the use of the needle vortex generators along the leading edge of the delta wing makes the vorticessmaller and closer to the wing surface. By moving from the front of the wing to the back of the wing or increasing the angle of attack, the vortex become larger and move away from the wing surface. Examination of the position and height of the primary andsecondary vortices by the results of the five-hole probe shows that the secondary vortex forms at the leading edge and near the wing surface, and it is much smaller than the primary vortex.The needle vortex generators on the leading edge produce small vortices that transfer energy to the main vortex on the wing, delaying the vortex breakdown. In general, the use of a vortex generator increases the lift force produced by the wing due to bringing the low pressure region of the vortex core closer to the wingsurface and thus reducing the pressure on the wing surface. In addition, the needle vortex generators reduce the wake area by reducing the vortex diameter on the wing surface, thereby reducing the wing drag force. The results of flow visualization show that when a vortex breakdown occurs, the vortex splits into several smaller vortices with opposite directions. Examination of the hot wire flowmeter results showed that by moving from the front of the wing to the rear of the wing, the speed fluctuations for the simple delta wing reduce, while the speed fluctuations for the delta wing equipped with the needle vortex generator remain almost constant. In fact, the needle vortex generators increase the turbulence energy of the flow.Keywords:Delta wing, Pressursensor, Vortex, Vortexbreakdown,Wind tunnel, Needle vortex generator, Smoke and laser flow visualization, Five-holeprobe, Hot wire flow meter